Four peptide hydrolases which have been isolated from the purified brush borders of human intestinal mucosa will be further purified by means of ion exchange chromatography on DEAE-cellulose, and acrylamide gel electrophoresis. Properties of the isolated enzymes including pH optima, stability, metal ion activation, and substrate specificity will be determined. The most descriminating substrate for each of the 4 isolated enzymes will be used to determine the level of activity of each enzyme in the brush border of per oral intestinal biopsies from patients with various diseases of undetermined etiology. The methods for measuring brush border peptide hydrolases in biopsy specimens will be the same as previously reported by this laboratory. Further studies of the metal ion requirements and substrate specificity of brush border peptide hydrolase IIb isolated from the rat intestinal mucosa will be carried out in an effort to obtain information which will make it possible to predict which peptide, among the hundreds not yet tested, are likely to be hydrolyzed by this enzyme. These studies may also provide a guide for doing similar studies on other rat and human peptide hydrolases. Finally, studies of the rate of absorption of the reducing and the non-reducing moiety of maltose will be performed to further define the details of disaccharide absorption by the small intestine which can then be compared with the previously determined characteristics of absorption of the double-labeled dipeptide phenyl alanyl phenalanine.